Re: Your change to function.c

["David S. Miller" <davem at dm dot cobaltmicro dot com>]

   Date: Mon, 05 Oct 1998 08:54:15 -0600
   From: Jeffrey A Law <law@cygnus.com>

     >    (set (reg:QI) (addressof:SI (reg:SF xxx)))

   But why would we ever want to get something like the above -- addressof is
   an address right?  Why would we ever look at it in a mode like QImode?

   What am I missing?

Look at the RTL you get while compiling libchill, specifically
format.c:inpconv().  The address of a float is taken, and cast to a
char pointer, and 4 bytes are picked out of it by the MOV4() macro.
The relevant stuff is:

#define MOV4(tgt,src) \
  *((char*)(tgt)  ) = *((char*)(src)  ), \
  *((char*)(tgt)+1) = *((char*)(src)+1), \
  *((char*)(tgt)+2) = *((char*)(src)+2), \
  *((char*)(tgt)+3) = *((char*)(src)+3)

float fval;
MOV4(io.__t.__locreal,&fval);

Look at what purge_addressof_1 looks at when this is compiled.  It
look at something resembling:

(insn 18 15 19 (set (reg:QI 110)
        (mem:QI (addressof:SI (reg:SF 108) 107) 0)) -1 (nil)
    (nil))

And this is the source of the problem cases on big endian.

Later,
David S. Miller
davem@dm.cobaltmicro.com